This invention relates to a spinal implant connection between a spinal rod and a vertebral anchor, and more particularly relates to a spinal implant connection with a clevis to attach to the vertebral anchor.
Spinal implant systems provide a rod for supporting the spine and for properly positioning components of the spine for various treatment purposes. Bolts, screws, and hooks are typically secured to the vertebrae for connection to the supporting rod. These vertebral anchors must frequently be positioned at various angles due the anatomical structure of the patient, the physiological problem being treated, and the preference of the physician. It is difficult to provide secure connections between the spinal support rod and these vertebral anchors at all the various angles that are required, especially where there are different distances between the rod and bolts and where these components are located at different heights on the patient.
One solution to this problem is shown in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson, the disclosures of which are specifically incorporated into this specification by reference. These patents describe a connection between a rod and a vertebral anchor, through which a surgeon may vary the angle between a spinal rod and the anchor to which the rod is attached. The connection is equipped with an interlocking set of washers that allow the surgeon to fix the desired angle between the anchor and the rod. In general, this system requires the surgeon in a typical installation to either sacrifice the capsule of the facet joint that may reside next to the connection, or elevate the connection above the facet joint and thereby raise the profile of the entire spinal implant system at that location. Occasionally, however, the surgeon may not wish to exercise either of these options in a particular surgery. Hence, an improvement over the device shown in these earlier patents would be a connection assembly that simultaneously minimizes the profile of the spinal implant system above the patient""s spine without generally requiring the surgeon to sacrifice a facet joint that may reside next to a particular rod-to-vertebral-anchor connection assembly. The following invention is one solution to that need.
In one aspect, this invention is a connection assembly between a spinal implant rod and a vertebral anchor. The assembly has a bolt with an aperture for receiving a portion of the spinal implant rod at one end. The assembly also has a clevis. The clevis defines a bore to hold a portion of the vertebral anchor and the ears of the clevis have holes through which the bolt is located with the bolt rotably connected to the ears. The assembly also has a rod interface washer positioned over a portion of the bolt, between the aperture of the bolt and the inside ear of the clevis. The rod interface washer is partly movable between the aperture of the bolt and the clevis, but the washer is fixed against rotating in relation to the bolt. Finally, the assembly also includes a compression member, such as a screw, that forceably engages or threads into the side of the bolt and continues into the aperture of the bolt. The screw is used to push the rod toward the vertebral anchor so that the inside and outside ears of the clevis are pressed together and the clevis is tightened around the vertebral anchor.
Optionally, the inside ear of the clevis and the rod interface washer have mating male protrusions and female cavities on their surfaces such that, when pressed together, the protrusions and cavities engage to further prevent rotation of the clevis in relation to the rod interface washer. In this alternative design, the protrusions and cavities have multiple interlocking orientations so that the rod interface washer and the clevis can be interlocked in a plurality of fixed angles in relation to each other.
An object of this invention is to reduce the physical mass that is typically required to attach a spinal rod to a vertebral anchor.
An advantage of this invention is that the clevis allows a vertebral anchor to be placed closer to the spinal rod than prior art designs that also use a single means to allow the surgeon to secure both the anchor and the rod to the connection assembly in one tightening step.
A feature of this invention is that it allows the surgeon the option of lowering the profile of a spinal attachment system closer to the spine without requiring the surgeon to sacrifice the capsule of a facet joint that may reside next to the connection assembly. In other words, this invention allows the connection assembly to be placed in a position that is medial to the facet joint.
As used in this specification the term xe2x80x9cclevisxe2x80x9d is used in its ordinary and accustomed meaning that beingxe2x80x94xe2x80x9c(1): a fitting for attaching or suspending parts (as a cable to another structural member of a bridge or a hanger for supporting pipe) that consists usu. of a U-shaped piece of metal with the ends drilled to receive a pin or bolt (2): any of various connections in which one part is fitted between the forked ends of another and fastened by means of a bolt or pin passing through the forked ends.xe2x80x9d Webster""s Third New International Dictionary, Unabridged. 